Method of enhancing the quality of high-moisture materials using system heat sources

Abstract

The present invention harvests and utilizes fluidized bed drying technology and waste heat streams augmented by other available heat sources to dry feedstock or fuel. This method is useful in many industries, including coal-fired power plants. Coal is dried using the present invention before it goes to coal pulverizers and on to the furnace / boiler arrangement. Coal can be intercepted on current coal feed systems ahead of the pulverizers. Drying fuel, such as coal, is done to improve boiler efficiency and reduce emissions. A two-stage bed utilized in the process first “pre-dries and separates” the feed stream into desirable and undesirable feedstock. Then, it incrementally dries and segregates fluidizable and non-fluidizable material from the product stream. This is all completed in a low-temperature, open-air system. Elevation of fan room air temperature is also accomplished using waste heat, thereby making available to the plant system higher temperature media to enhance the feedstock drying process.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. provisional application Ser. No. 60 / 618,379 filed on Oct. 12, 2004, which is hereby incorporated by reference.FIELD OF THE INVENTION [0002] This invention relates to the use of existing system sources of waste heat available at a typical industrial process plant to enhance the quality of materials constituting a feedstock or combustion source for that plant. More specifically, the invention utilizes existing plant waste heat sources in a low-temperature, open-air process to dry such materials to improve their thermal content or processibility and reduce plant emissions before the particulate material is processed or combusted at the plant. While this process may be utilized in many varied industries in an efficient and economical manner, it is particularly well suited for use in electric power generation plants for reducing moisture content in coal before it is fired. BACKGROUND OF THE INVENTIO...

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Benefits of technology

[0027] Although the invention has application to many varied industries, for illustrative purposes, the invention is described herein with respect to a typical coal-burning electric power generating plant, where removal of some of the moisture from the coal in a dryer is desirable for improving the heat value of the coal and the resulting boiler efficiency of the plant. Drying coal in this manner can enhance or even enable the use of low-rank coals like subbituminous and lignite coals. By reducing the moisture content of the coal, regardless of whether it constitutes low-rank or high-rank coal, other enhanced operating efficiencies may be realized, as well. For example, drier coal will reduce the burden on the coal handling system, conveyers and coal crushers in the electric generating plant. Since drier coal is easier to convey, this reduces maintenance costs and increases availability of the coal handling system. Drier coal is also easier to pulverize, so less “mill” power is needed to achieve the same grind size (coal fineness). With less fuel moisture, moisture content leaving the mill is reduced. This will improve the results of grinding of the coal. Additionally, less primary air used to convey, fluidize, and heat the coal is needed. Such lower levels of primary air reduces air velocities and with lower primary air velocities, there is a significant reduction of erosion in coal mills, coal transfer pipes, coal burners, and associated equipment. This has the effect of reducing coal transfer pipe and mill maintenance costs, which are, for lignite-fired plants, very high. Reductions in stack emissions should also be realized, thereby improving collection efficiency of downstream environmental protection equipment.

[0035] The present invention also provides a system for removing fly ash, sulfur, mercury-bearing material, and other harmful pollutants from the coal using the material segregation and sorting capabilities of fluidized beds, in contrast to current prior art systems that attempt to remove the pollutants and other contaminates after the coal has been burned. Removal of such pollutants and other contaminants before the coal is burned eliminates potential harm that may be caused to the environment by the contaminants in the plant processes, with the expected benefits of lower emissions, coal input levels, auxiliary power needs to operate the plant, plant water usage, equipment maintenance costs caused by metal erosion and other factors, and capital costs arising from equipment needed to extract these contaminants from the flue gas.

Problems solved by technology

For many existing turbines, this could reduce power output and have an adverse impact on performance of turbine stages downstream from the extraction point, making this source for heat extraction of limited desirability.

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